1. Field of the Invention
The invention concerns an arrangement to prevent the intrusion of foreign matter, in particular cerumen, into an electro-acoustical transducer.
2. Technical Backoround
From DE-AS 12 63 849, an arrangement is known for an in-the-ear hearing aid to prevent the intrusion of cerumen (ear wax) into a transducer, which is designed as a hollow member in cap form (ear insert) of elastic material that can be attached to the sound exit nozzle (projection) of a hearing aid, that in its interior presents a chamber-like expansion of a bore for the passage of the sound at its hemispherically-shaped end, in which a layer of porous, sound-permeable material is arranged. Given pore sizes of about 0.2 to 0.5 mm and partitions that are thin by comparison, in order to achieve a great density of pores per surface unit, the porous layer is of relatively great thickness approximately corresponding to the inside cylindrical radius of the hollow member. The wall thickness of the hollow member amounts to about one seventh of the outside cylindrical diameter. It is thus relatively thick. Altogether, this arrangement results in much space being required, especially in the direction of travel of the sound. Besides, two separate components are required to close the sound exit nozzle against the infiltration of cerumen, wherein the hollow member acts as a mounting support (added arrangement) for the porous layer, which in turn prevents the intrusion of cerumen and must be replaced regularly since a cleaning of this porous and hence soft material is not possible.
From DE-GM 84 36 783 and 85 04 765, sieve-like perforated caps are known that can be screwed or snapped into or onto projections that extend from the hearing aid housing as an extension of the sound channel only for this purpose.
The penetration of cerumen into the sound channel is largely prevented by the introduction of recesses (grooves) on the housing outside the sound channel. The outer projection needed only for the mounting of the perforated caps is an added arrangement and necessitates a relatively great length in construction in the direction of the sound propagation, even more and markedly increased by the thickness of the perforated caps projecting from the extensions, especially since the thickness of their walls is on the order of the sieve-like openings. Beyond this, the large number of openings arranged in a sieve-like manner increases the danger of penetration by cerumen.
The object of the present invention is to design an arrangement of the type initially indicated, in such a manner that it will occupy less space and be of simpler construction compared with the state of the art.